(RealSimple.com) -- When to spend and when to save on eight essentials that affect your health every day.

Thermometers

Old-school mercury versions, which are hard to read and can break, have gone the way of the Walkman. An inexpensive digital thermometer (about $6) is the new classic and more than adequate for the average person.

Two things to look for: a big, backlit display that's easy to see in a dark room, and a fast reading time of about 15 seconds, says Caroline Dorsen, a board-certified family nurse practitioner in New York City. Go for an under-the-tongue variety, as ear (or tympanic) thermometers are less reliable. A study done at the Stollery Children's Hospital in Edmonton, Alberta, found that parents using home tympanic models failed to detect a fever 25 percent of the time. If you have to check someone's temperature hourly, invest in a temporal artery (forehead) thermometer. It's even easier to use but a bit more expensive (about $35).

For those who are young or who need only low-magnification nonprescription glasses to read, the lenses in specs that cost less than a few lattes (about $15) will be as effective as those costing as much as a cappuccino machine (more than $125).

That said, if the distance between your eyes, known as your pupillary distance (PD), is unusually narrow or wide, budget glasses may not be comfortable, since their magnification is focused in the center of each lens. "You won't damage your eyes by wearing them, but you may get a headache," says James Salz, M.D., a Los Angeles based spokesperson for the American Academy of Ophthalmology. And as you age, your PD becomes more important. So if you do have an unusual one, you may find that prescription glasses are more effective.

Bathroom Scales

A basic, inexpensive analog scale ($10 and up), the kind that uses a needle pointer, suffices for most people, says Lara Sutton, RD, a nutritionist for Sports Club/LA in New York City. Look for one with a display you can clearly read while standing up and a platform on which your feet fit completely.

If you really sweat the details, choose a digital scale that can chart 0.1-pound increments. That said, if you're serious about weight loss or you're an athlete, consider a costlier scale ($30 and up) that measures body-fat percentages, too. "This type of reading can help you see if you're building muscle and getting fitter," says Gregory Florez, a spokesperson for the America Council on Exercise who is based in Salt Lake City. While the body-fat calculation isn't 100 percent accurate, if you use the feature regularly, the readings will still help you to track your progress.

Sure, you could pump a fine, 80 degree, lavender-infused mist into the air with a fancy humidifier, but it's not necessary; a standard model (about $40) has everything you need.

The only factor to consider is temperature, says Dorsen: "If you have small children or pets, don't get a vaporizer version that spits warm mist into the air, because it can burn delicate skin" (and inquisitive snouts). In homes without kids or pets, the temperature choice is yours. "There haven't been any studies that relate mist temperature to effectiveness," she says. If your water has a high mineral content, however, opt for a more expensive evaporative model or a vaporizer. The Environmental Protection Agency has found that basic humidifiers are prone to dispersing those minerals into the air, which can irritate lungs. An alternative: Use distilled water in any style humidifier.

Dental Floss

Most people find that inexpensive waxed floss makes this chore easy and a little more pain-free than just-as-economical unwaxed floss. "It slides comfortably between most teeth and doesn't fray as much as unwaxed floss does," says Charles K. Perle, D.M.D., a spokesperson for the Academy of General Dentistry and a dentist in Jersey City, New Jersey. But if your teeth are spaced closely together or if you have old fillings that have expanded, you may want to spend an extra dollar or two on smooth, snag-resistant dental floss or tape (thin, flat floss). It glides between tight teeth even more easily and can be more gentle on gyms than waxed floss.

The most low-budget yet effective option is a rubber hot-water bottle, which can conform to any part of the body and never needs to be turned off. It does lose heat over time, however. So if you need prolonged heat or don't want to deal with heating water, a wallet-friendly electric heating pad is a better choice.

There are only three features it needs, which are standard to most pads in the $15 price ranges, says Roger Herr, a Seattle-based spokesperson for the American Physical Therapy Association: a size big enough to heat your back but small enough to wrap around an ankle; a soft cotton cover, so skin doesn't get burned or irritated; and at least two temperature settings. Why two? Smaller areas of the body, like your hands, feet, and head, can tolerate higher temperatures for longer than larger areas of the body, which need a lower heat setting. Pricier pads with extras such as moist heat don't offer added benefits, so they're generally not worth the expense.

If you got your pedometer via a kids' meal or a cereal box, don't count on it to tally steps accurately or for long. Dan Heil, Ph.D., an exercise physiologist and researcher at Montana Sate University, in Bozeman, found that pedometers that gauge movement with a flimsy mechanism called a hairspring and that cost less than $15 often wear out within six months. He also found that pedometers driven electronically or via a more substantial coiled spring, and which cost about $25, are considerably more accurate at counting steps. However, he warns, "distance, speed, and calories-burned measurements have a tendency to be inaccurate no matter how much a pedometer costs." So skip those kinds of features, which are found on the most expensive models.

The American Dental Association maintains that both budget-friendly manual and pricier power brushes can effectively clean teeth, so the choice is yours. Whatever type you prefer to use, avoid a toothbrush with hard, stiff bristles, which can cause enamel erosion, tooth sensitivity, and receding gyms. "The best option is a soft brush with nylon bristles that have rounded ends," says Perle. Additional features that you pay for, like ridged bristles or an indicator that signals when it's time to trade in a brush, don't aid in oral health, though they may make caring for your teeth more comfortable or help you to remember to replace your brush after three months. If you prefer an electric brush, opt for the oscillating-rotating kind. A 2003 review by the nonprofit Cochrane Collaboration Oral Health group, in Manchester, England, found that these models provide a modest benefit in reducing plaque and gingivitis compared with manual brushes.